1. Technical Field
The present invention relates to a combination valve for pressure control and venting in a fuel system for delivering fuel to an internal combustion engine, comprising a primary valve cone, which is supported so that it is displaceable between two limit positions in a cylinder bore in a valve housing, against the action of a spring element, the displacement of the valve cone from an inoperative limit position into an operative limit position leading to the opening of a connection between an inlet duct and an outlet duct in the valve housing. The invention also relates to a fuel system for use of the combination valve.
2. Background
Fuel systems for diesel engines use relatively high working pressures. If air gets into the fuel system on the high-pressure side, it is not possible to maintain the required working pressure. Engine operating problems can also arise if the fuel has a high water content. Fuel systems for diesel engines are usually provided with venting screw and hand pump, which can be used to vent air and drain water from the fuel system. The method of removing air or water by means of venting screw and hand pump is time-consuming and awkward.
Fuel systems exist which have arrangements for automating the process of removing air or water, as disclosed, for example, by U.S. Pat. No. 5,534,161. This patent describes a pump which can be driven in two directions by means of a microprocessor for use in removing water from a fuel system. However, this arrangement only facilitates the process of venting air from the fuel system, and further measures are required in order to remove air from the high-pressure side of the system. This arrangement means, therefore, that the number of fuel system components is increased without entirely solving the problem by facilitating the process of venting air.